/*
 * Copyright (C) 2002 Roman Zippel <zippel@linux-m68k.org>
 * Released under the terms of the GNU GPL v2.0.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "lkc.h"

#define DEBUG_EXPR    0

static int expr_eq(struct expr *e1, struct expr *e2);
static struct expr *expr_eliminate_yn(struct expr *e);
static struct expr *expr_extract_eq_and(struct expr **ep1, struct expr **ep2);
static struct expr *expr_extract_eq_or(struct expr **ep1, struct expr **ep2);
static void expr_extract_eq(enum expr_type type, struct expr **ep, struct expr **ep1, struct expr **ep2);

struct expr *expr_alloc_symbol(struct symbol *sym)
{
    struct expr *e = xcalloc(1, sizeof(*e));
    e->type = E_SYMBOL;
    e->left.sym = sym;
    return e;
}

struct expr *expr_alloc_one(enum expr_type type, struct expr *ce)
{
    struct expr *e = xcalloc(1, sizeof(*e));
    e->type = type;
    e->left.expr = ce;
    return e;
}

struct expr *expr_alloc_two(enum expr_type type, struct expr *e1, struct expr *e2)
{
    struct expr *e = xcalloc(1, sizeof(*e));
    e->type = type;
    e->left.expr = e1;
    e->right.expr = e2;
    return e;
}

struct expr *expr_alloc_comp(enum expr_type type, struct symbol *s1, struct symbol *s2)
{
    struct expr *e = xcalloc(1, sizeof(*e));
    e->type = type;
    e->left.sym = s1;
    e->right.sym = s2;
    return e;
}

struct expr *expr_alloc_and(struct expr *e1, struct expr *e2)
{
    if (!e1)
        return e2;
    return e2 ? expr_alloc_two(E_AND, e1, e2) : e1;
}

struct expr *expr_alloc_or(struct expr *e1, struct expr *e2)
{
    if (!e1)
        return e2;
    return e2 ? expr_alloc_two(E_OR, e1, e2) : e1;
}

struct expr *expr_copy(const struct expr *org)
{
    struct expr *e;

    if (!org)
        return NULL;

    e = xmalloc(sizeof(*org));
    memcpy(e, org, sizeof(*org));
    switch (org->type) {
    case E_SYMBOL:
        e->left = org->left;
        break;
    case E_NOT:
        e->left.expr = expr_copy(org->left.expr);
        break;
    case E_EQUAL:
    case E_UNEQUAL:
        e->left.sym = org->left.sym;
        e->right.sym = org->right.sym;
        break;
    case E_AND:
    case E_OR:
    case E_LIST:
        e->left.expr = expr_copy(org->left.expr);
        e->right.expr = expr_copy(org->right.expr);
        break;
    default:
        printf("can't copy type %d\n", e->type);
        free(e);
        e = NULL;
        break;
    }

    return e;
}

void expr_free(struct expr *e)
{
    if (!e)
        return;

    switch (e->type) {
    case E_SYMBOL:
        break;
    case E_NOT:
        expr_free(e->left.expr);
        return;
    case E_EQUAL:
    case E_UNEQUAL:
        break;
    case E_OR:
    case E_AND:
        expr_free(e->left.expr);
        expr_free(e->right.expr);
        break;
    default:
        printf("how to free type %d?\n", e->type);
        break;
    }
    free(e);
}

static int trans_count;

#define e1 (*ep1)
#define e2 (*ep2)

static void __expr_eliminate_eq(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
    if (e1->type == type) {
        __expr_eliminate_eq(type, &e1->left.expr, &e2);
        __expr_eliminate_eq(type, &e1->right.expr, &e2);
        return;
    }
    if (e2->type == type) {
        __expr_eliminate_eq(type, &e1, &e2->left.expr);
        __expr_eliminate_eq(type, &e1, &e2->right.expr);
        return;
    }
    if (e1->type == E_SYMBOL && e2->type == E_SYMBOL &&
        e1->left.sym == e2->left.sym &&
        (e1->left.sym == &symbol_yes || e1->left.sym == &symbol_no))
        return;
    if (!expr_eq(e1, e2))
        return;
    trans_count++;
    expr_free(e1); expr_free(e2);
    switch (type) {
    case E_OR:
        e1 = expr_alloc_symbol(&symbol_no);
        e2 = expr_alloc_symbol(&symbol_no);
        break;
    case E_AND:
        e1 = expr_alloc_symbol(&symbol_yes);
        e2 = expr_alloc_symbol(&symbol_yes);
        break;
    default:
        ;
    }
}

void expr_eliminate_eq(struct expr **ep1, struct expr **ep2)
{
    if (!e1 || !e2)
        return;
    switch (e1->type) {
    case E_OR:
    case E_AND:
        __expr_eliminate_eq(e1->type, ep1, ep2);
    default:
        ;
    }
    if (e1->type != e2->type) switch (e2->type) {
    case E_OR:
    case E_AND:
        __expr_eliminate_eq(e2->type, ep1, ep2);
    default:
        ;
    }
    e1 = expr_eliminate_yn(e1);
    e2 = expr_eliminate_yn(e2);
}

#undef e1
#undef e2

static int expr_eq(struct expr *e1, struct expr *e2)
{
    int res, old_count;

    if (e1->type != e2->type)
        return 0;
    switch (e1->type) {
    case E_EQUAL:
    case E_UNEQUAL:
        return e1->left.sym == e2->left.sym && e1->right.sym == e2->right.sym;
    case E_SYMBOL:
        return e1->left.sym == e2->left.sym;
    case E_NOT:
        return expr_eq(e1->left.expr, e2->left.expr);
    case E_AND:
    case E_OR:
        e1 = expr_copy(e1);
        e2 = expr_copy(e2);
        old_count = trans_count;
        expr_eliminate_eq(&e1, &e2);
        res = (e1->type == E_SYMBOL && e2->type == E_SYMBOL &&
               e1->left.sym == e2->left.sym);
        expr_free(e1);
        expr_free(e2);
        trans_count = old_count;
        return res;
    case E_LIST:
    case E_RANGE:
    case E_NONE:
        /* panic */;
    }

    if (DEBUG_EXPR) {
        expr_fprint(e1, stdout);
        printf(" = ");
        expr_fprint(e2, stdout);
        printf(" ?\n");
    }

    return 0;
}

static struct expr *expr_eliminate_yn(struct expr *e)
{
    struct expr *tmp;

    if (e) switch (e->type) {
    case E_AND:
        e->left.expr = expr_eliminate_yn(e->left.expr);
        e->right.expr = expr_eliminate_yn(e->right.expr);
        if (e->left.expr->type == E_SYMBOL) {
            if (e->left.expr->left.sym == &symbol_no) {
                expr_free(e->left.expr);
                expr_free(e->right.expr);
                e->type = E_SYMBOL;
                e->left.sym = &symbol_no;
                e->right.expr = NULL;
                return e;
            } else if (e->left.expr->left.sym == &symbol_yes) {
                free(e->left.expr);
                tmp = e->right.expr;
                *e = *(e->right.expr);
                free(tmp);
                return e;
            }
        }
        if (e->right.expr->type == E_SYMBOL) {
            if (e->right.expr->left.sym == &symbol_no) {
                expr_free(e->left.expr);
                expr_free(e->right.expr);
                e->type = E_SYMBOL;
                e->left.sym = &symbol_no;
                e->right.expr = NULL;
                return e;
            } else if (e->right.expr->left.sym == &symbol_yes) {
                free(e->right.expr);
                tmp = e->left.expr;
                *e = *(e->left.expr);
                free(tmp);
                return e;
            }
        }
        break;
    case E_OR:
        e->left.expr = expr_eliminate_yn(e->left.expr);
        e->right.expr = expr_eliminate_yn(e->right.expr);
        if (e->left.expr->type == E_SYMBOL) {
            if (e->left.expr->left.sym == &symbol_no) {
                free(e->left.expr);
                tmp = e->right.expr;
                *e = *(e->right.expr);
                free(tmp);
                return e;
            } else if (e->left.expr->left.sym == &symbol_yes) {
                expr_free(e->left.expr);
                expr_free(e->right.expr);
                e->type = E_SYMBOL;
                e->left.sym = &symbol_yes;
                e->right.expr = NULL;
                return e;
            }
        }
        if (e->right.expr->type == E_SYMBOL) {
            if (e->right.expr->left.sym == &symbol_no) {
                free(e->right.expr);
                tmp = e->left.expr;
                *e = *(e->left.expr);
                free(tmp);
                return e;
            } else if (e->right.expr->left.sym == &symbol_yes) {
                expr_free(e->left.expr);
                expr_free(e->right.expr);
                e->type = E_SYMBOL;
                e->left.sym = &symbol_yes;
                e->right.expr = NULL;
                return e;
            }
        }
        break;
    default:
        ;
    }
    return e;
}

/*
 * bool FOO!=n => FOO
 */
struct expr *expr_trans_bool(struct expr *e)
{
    if (!e)
        return NULL;
    switch (e->type) {
    case E_AND:
    case E_OR:
    case E_NOT:
        e->left.expr = expr_trans_bool(e->left.expr);
        e->right.expr = expr_trans_bool(e->right.expr);
        break;
    case E_UNEQUAL:
        // FOO!=n -> FOO
        if (e->left.sym->type == S_TRISTATE) {
            if (e->right.sym == &symbol_no) {
                e->type = E_SYMBOL;
                e->right.sym = NULL;
            }
        }
        break;
    default:
        ;
    }
    return e;
}

/*
 * e1 || e2 -> ?
 */
static struct expr *expr_join_or(struct expr *e1, struct expr *e2)
{
    struct expr *tmp;
    struct symbol *sym1, *sym2;

    if (expr_eq(e1, e2))
        return expr_copy(e1);
    if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL && e1->type != E_NOT)
        return NULL;
    if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL && e2->type != E_NOT)
        return NULL;
    if (e1->type == E_NOT) {
        tmp = e1->left.expr;
        if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL && tmp->type != E_SYMBOL)
            return NULL;
        sym1 = tmp->left.sym;
    } else
        sym1 = e1->left.sym;
    if (e2->type == E_NOT) {
        if (e2->left.expr->type != E_SYMBOL)
            return NULL;
        sym2 = e2->left.expr->left.sym;
    } else
        sym2 = e2->left.sym;
    if (sym1 != sym2)
        return NULL;
    if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
        return NULL;
    if (sym1->type == S_TRISTATE) {
        if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
            ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
             (e1->right.sym == &symbol_mod && e2->right.sym == &symbol_yes))) {
            // (a='y') || (a='m') -> (a!='n')
            return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_no);
        }
        if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
            ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
             (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes))) {
            // (a='y') || (a='n') -> (a!='m')
            return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_mod);
        }
        if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
            ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
             (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod))) {
            // (a='m') || (a='n') -> (a!='y')
            return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_yes);
        }
    }
    if (sym1->type == S_BOOLEAN && sym1 == sym2) {
        if ((e1->type == E_NOT && e1->left.expr->type == E_SYMBOL && e2->type == E_SYMBOL) ||
            (e2->type == E_NOT && e2->left.expr->type == E_SYMBOL && e1->type == E_SYMBOL))
            return expr_alloc_symbol(&symbol_yes);
    }

    if (DEBUG_EXPR) {
        printf("optimize (");
        expr_fprint(e1, stdout);
        printf(") || (");
        expr_fprint(e2, stdout);
        printf(")?\n");
    }
    return NULL;
}

static struct expr *expr_join_and(struct expr *e1, struct expr *e2)
{
    struct expr *tmp;
    struct symbol *sym1, *sym2;

    if (expr_eq(e1, e2))
        return expr_copy(e1);
    if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL && e1->type != E_NOT)
        return NULL;
    if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL && e2->type != E_NOT)
        return NULL;
    if (e1->type == E_NOT) {
        tmp = e1->left.expr;
        if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL && tmp->type != E_SYMBOL)
            return NULL;
        sym1 = tmp->left.sym;
    } else
        sym1 = e1->left.sym;
    if (e2->type == E_NOT) {
        if (e2->left.expr->type != E_SYMBOL)
            return NULL;
        sym2 = e2->left.expr->left.sym;
    } else
        sym2 = e2->left.sym;
    if (sym1 != sym2)
        return NULL;
    if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
        return NULL;

    if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_yes) ||
        (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_yes))
        // (a) && (a='y') -> (a='y')
        return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

    if ((e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_no) ||
        (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_no))
        // (a) && (a!='n') -> (a)
        return expr_alloc_symbol(sym1);

    if ((e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_mod) ||
        (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_mod))
        // (a) && (a!='m') -> (a='y')
        return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

    if (sym1->type == S_TRISTATE) {
        if (e1->type == E_EQUAL && e2->type == E_UNEQUAL) {
            // (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
            sym2 = e1->right.sym;
            if ((e2->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
                return sym2 != e2->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
                                 : expr_alloc_symbol(&symbol_no);
        }
        if (e1->type == E_UNEQUAL && e2->type == E_EQUAL) {
            // (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
            sym2 = e2->right.sym;
            if ((e1->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
                return sym2 != e1->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
                                 : expr_alloc_symbol(&symbol_no);
        }
        if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
               ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
                (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes)))
            // (a!='y') && (a!='n') -> (a='m')
            return expr_alloc_comp(E_EQUAL, sym1, &symbol_mod);

        if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
               ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
                (e1->right.sym == &symbol_mod && e2->right.sym == &symbol_yes)))
            // (a!='y') && (a!='m') -> (a='n')
            return expr_alloc_comp(E_EQUAL, sym1, &symbol_no);

        if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
               ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
                (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod)))
            // (a!='m') && (a!='n') -> (a='m')
            return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

        if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_mod) ||
            (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_mod) ||
            (e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_yes) ||
            (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_yes))
            return NULL;
    }

    if (DEBUG_EXPR) {
        printf("optimize (");
        expr_fprint(e1, stdout);
        printf(") && (");
        expr_fprint(e2, stdout);
        printf(")?\n");
    }
    return NULL;
}

static void expr_eliminate_dups1(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
#define e1 (*ep1)
#define e2 (*ep2)
    struct expr *tmp;

    if (e1->type == type) {
        expr_eliminate_dups1(type, &e1->left.expr, &e2);
        expr_eliminate_dups1(type, &e1->right.expr, &e2);
        return;
    }
    if (e2->type == type) {
        expr_eliminate_dups1(type, &e1, &e2->left.expr);
        expr_eliminate_dups1(type, &e1, &e2->right.expr);
        return;
    }
    if (e1 == e2)
        return;

    switch (e1->type) {
    case E_OR: case E_AND:
        expr_eliminate_dups1(e1->type, &e1, &e1);
    default:
        ;
    }

    switch (type) {
    case E_OR:
        tmp = expr_join_or(e1, e2);
        if (tmp) {
            expr_free(e1); expr_free(e2);
            e1 = expr_alloc_symbol(&symbol_no);
            e2 = tmp;
            trans_count++;
        }
        break;
    case E_AND:
        tmp = expr_join_and(e1, e2);
        if (tmp) {
            expr_free(e1); expr_free(e2);
            e1 = expr_alloc_symbol(&symbol_yes);
            e2 = tmp;
            trans_count++;
        }
        break;
    default:
        ;
    }
#undef e1
#undef e2
}

static void expr_eliminate_dups2(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
#define e1 (*ep1)
#define e2 (*ep2)
    struct expr *tmp, *tmp1, *tmp2;

    if (e1->type == type) {
        expr_eliminate_dups2(type, &e1->left.expr, &e2);
        expr_eliminate_dups2(type, &e1->right.expr, &e2);
        return;
    }
    if (e2->type == type) {
        expr_eliminate_dups2(type, &e1, &e2->left.expr);
        expr_eliminate_dups2(type, &e1, &e2->right.expr);
    }
    if (e1 == e2)
        return;

    switch (e1->type) {
    case E_OR:
        expr_eliminate_dups2(e1->type, &e1, &e1);
        // (FOO || BAR) && (!FOO && !BAR) -> n
        tmp1 = expr_transform(expr_alloc_one(E_NOT, expr_copy(e1)));
        tmp2 = expr_copy(e2);
        tmp = expr_extract_eq_and(&tmp1, &tmp2);
        if (expr_is_yes(tmp1)) {
            expr_free(e1);
            e1 = expr_alloc_symbol(&symbol_no);
            trans_count++;
        }
        expr_free(tmp2);
        expr_free(tmp1);
        expr_free(tmp);
        break;
    case E_AND:
        expr_eliminate_dups2(e1->type, &e1, &e1);
        // (FOO && BAR) || (!FOO || !BAR) -> y
        tmp1 = expr_transform(expr_alloc_one(E_NOT, expr_copy(e1)));
        tmp2 = expr_copy(e2);
        tmp = expr_extract_eq_or(&tmp1, &tmp2);
        if (expr_is_no(tmp1)) {
            expr_free(e1);
            e1 = expr_alloc_symbol(&symbol_yes);
            trans_count++;
        }
        expr_free(tmp2);
        expr_free(tmp1);
        expr_free(tmp);
        break;
    default:
        ;
    }
#undef e1
#undef e2
}

struct expr *expr_eliminate_dups(struct expr *e)
{
    int oldcount;
    if (!e)
        return e;

    oldcount = trans_count;
    while (1) {
        trans_count = 0;
        switch (e->type) {
        case E_OR: case E_AND:
            expr_eliminate_dups1(e->type, &e, &e);
            expr_eliminate_dups2(e->type, &e, &e);
        default:
            ;
        }
        if (!trans_count)
            break;
        e = expr_eliminate_yn(e);
    }
    trans_count = oldcount;
    return e;
}

struct expr *expr_transform(struct expr *e)
{
    struct expr *tmp;

    if (!e)
        return NULL;
    switch (e->type) {
    case E_EQUAL:
    case E_UNEQUAL:
    case E_SYMBOL:
    case E_LIST:
        break;
    default:
        e->left.expr = expr_transform(e->left.expr);
        e->right.expr = expr_transform(e->right.expr);
    }

    switch (e->type) {
    case E_EQUAL:
        if (e->left.sym->type != S_BOOLEAN)
            break;
        if (e->right.sym == &symbol_no) {
            e->type = E_NOT;
            e->left.expr = expr_alloc_symbol(e->left.sym);
            e->right.sym = NULL;
            break;
        }
        if (e->right.sym == &symbol_mod) {
            printf("boolean symbol %s tested for 'm'? test forced to 'n'\n", e->left.sym->name);
            e->type = E_SYMBOL;
            e->left.sym = &symbol_no;
            e->right.sym = NULL;
            break;
        }
        if (e->right.sym == &symbol_yes) {
            e->type = E_SYMBOL;
            e->right.sym = NULL;
            break;
        }
        break;
    case E_UNEQUAL:
        if (e->left.sym->type != S_BOOLEAN)
            break;
        if (e->right.sym == &symbol_no) {
            e->type = E_SYMBOL;
            e->right.sym = NULL;
            break;
        }
        if (e->right.sym == &symbol_mod) {
            printf("boolean symbol %s tested for 'm'? test forced to 'y'\n", e->left.sym->name);
            e->type = E_SYMBOL;
            e->left.sym = &symbol_yes;
            e->right.sym = NULL;
            break;
        }
        if (e->right.sym == &symbol_yes) {
            e->type = E_NOT;
            e->left.expr = expr_alloc_symbol(e->left.sym);
            e->right.sym = NULL;
            break;
        }
        break;
    case E_NOT:
        switch (e->left.expr->type) {
        case E_NOT:
            // !!a -> a
            tmp = e->left.expr->left.expr;
            free(e->left.expr);
            free(e);
            e = tmp;
            e = expr_transform(e);
            break;
        case E_EQUAL:
        case E_UNEQUAL:
            // !a='x' -> a!='x'
            tmp = e->left.expr;
            free(e);
            e = tmp;
            e->type = e->type == E_EQUAL ? E_UNEQUAL : E_EQUAL;
            break;
        case E_OR:
            // !(a || b) -> !a && !b
            tmp = e->left.expr;
            e->type = E_AND;
            e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
            tmp->type = E_NOT;
            tmp->right.expr = NULL;
            e = expr_transform(e);
            break;
        case E_AND:
            // !(a && b) -> !a || !b
            tmp = e->left.expr;
            e->type = E_OR;
            e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
            tmp->type = E_NOT;
            tmp->right.expr = NULL;
            e = expr_transform(e);
            break;
        case E_SYMBOL:
            if (e->left.expr->left.sym == &symbol_yes) {
                // !'y' -> 'n'
                tmp = e->left.expr;
                free(e);
                e = tmp;
                e->type = E_SYMBOL;
                e->left.sym = &symbol_no;
                break;
            }
            if (e->left.expr->left.sym == &symbol_mod) {
                // !'m' -> 'm'
                tmp = e->left.expr;
                free(e);
                e = tmp;
                e->type = E_SYMBOL;
                e->left.sym = &symbol_mod;
                break;
            }
            if (e->left.expr->left.sym == &symbol_no) {
                // !'n' -> 'y'
                tmp = e->left.expr;
                free(e);
                e = tmp;
                e->type = E_SYMBOL;
                e->left.sym = &symbol_yes;
                break;
            }
            break;
        default:
            ;
        }
        break;
    default:
        ;
    }
    return e;
}

int expr_contains_symbol(struct expr *dep, struct symbol *sym)
{
    if (!dep)
        return 0;

    switch (dep->type) {
    case E_AND:
    case E_OR:
        return expr_contains_symbol(dep->left.expr, sym) ||
               expr_contains_symbol(dep->right.expr, sym);
    case E_SYMBOL:
        return dep->left.sym == sym;
    case E_EQUAL:
    case E_UNEQUAL:
        return dep->left.sym == sym ||
               dep->right.sym == sym;
    case E_NOT:
        return expr_contains_symbol(dep->left.expr, sym);
    default:
        ;
    }
    return 0;
}

bool expr_depends_symbol(struct expr *dep, struct symbol *sym)
{
    if (!dep)
        return false;

    switch (dep->type) {
    case E_AND:
        return expr_depends_symbol(dep->left.expr, sym) ||
               expr_depends_symbol(dep->right.expr, sym);
    case E_SYMBOL:
        return dep->left.sym == sym;
    case E_EQUAL:
        if (dep->left.sym == sym) {
            if (dep->right.sym == &symbol_yes || dep->right.sym == &symbol_mod)
                return true;
        }
        break;
    case E_UNEQUAL:
        if (dep->left.sym == sym) {
            if (dep->right.sym == &symbol_no)
                return true;
        }
        break;
    default:
        ;
    }
     return false;
}

static struct expr *expr_extract_eq_and(struct expr **ep1, struct expr **ep2)
{
    struct expr *tmp = NULL;
    expr_extract_eq(E_AND, &tmp, ep1, ep2);
    if (tmp) {
        *ep1 = expr_eliminate_yn(*ep1);
        *ep2 = expr_eliminate_yn(*ep2);
    }
    return tmp;
}

static struct expr *expr_extract_eq_or(struct expr **ep1, struct expr **ep2)
{
    struct expr *tmp = NULL;
    expr_extract_eq(E_OR, &tmp, ep1, ep2);
    if (tmp) {
        *ep1 = expr_eliminate_yn(*ep1);
        *ep2 = expr_eliminate_yn(*ep2);
    }
    return tmp;
}

static void expr_extract_eq(enum expr_type type, struct expr **ep, struct expr **ep1, struct expr **ep2)
{
#define e1 (*ep1)
#define e2 (*ep2)
    if (e1->type == type) {
        expr_extract_eq(type, ep, &e1->left.expr, &e2);
        expr_extract_eq(type, ep, &e1->right.expr, &e2);
        return;
    }
    if (e2->type == type) {
        expr_extract_eq(type, ep, ep1, &e2->left.expr);
        expr_extract_eq(type, ep, ep1, &e2->right.expr);
        return;
    }
    if (expr_eq(e1, e2)) {
        *ep = *ep ? expr_alloc_two(type, *ep, e1) : e1;
        expr_free(e2);
        if (type == E_AND) {
            e1 = expr_alloc_symbol(&symbol_yes);
            e2 = expr_alloc_symbol(&symbol_yes);
        } else if (type == E_OR) {
            e1 = expr_alloc_symbol(&symbol_no);
            e2 = expr_alloc_symbol(&symbol_no);
        }
    }
#undef e1
#undef e2
}

struct expr *expr_trans_compare(struct expr *e, enum expr_type type, struct symbol *sym)
{
    struct expr *e1, *e2;

    if (!e) {
        e = expr_alloc_symbol(sym);
        if (type == E_UNEQUAL)
            e = expr_alloc_one(E_NOT, e);
        return e;
    }
    switch (e->type) {
    case E_AND:
        e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
        e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
        if (sym == &symbol_yes)
            e = expr_alloc_two(E_AND, e1, e2);
        if (sym == &symbol_no)
            e = expr_alloc_two(E_OR, e1, e2);
        if (type == E_UNEQUAL)
            e = expr_alloc_one(E_NOT, e);
        return e;
    case E_OR:
        e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
        e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
        if (sym == &symbol_yes)
            e = expr_alloc_two(E_OR, e1, e2);
        if (sym == &symbol_no)
            e = expr_alloc_two(E_AND, e1, e2);
        if (type == E_UNEQUAL)
            e = expr_alloc_one(E_NOT, e);
        return e;
    case E_NOT:
        return expr_trans_compare(e->left.expr, type == E_EQUAL ? E_UNEQUAL : E_EQUAL, sym);
    case E_UNEQUAL:
    case E_EQUAL:
        if (type == E_EQUAL) {
            if (sym == &symbol_yes)
                return expr_copy(e);
            if (sym == &symbol_mod)
                return expr_alloc_symbol(&symbol_no);
            if (sym == &symbol_no)
                return expr_alloc_one(E_NOT, expr_copy(e));
        } else {
            if (sym == &symbol_yes)
                return expr_alloc_one(E_NOT, expr_copy(e));
            if (sym == &symbol_mod)
                return expr_alloc_symbol(&symbol_yes);
            if (sym == &symbol_no)
                return expr_copy(e);
        }
        break;
    case E_SYMBOL:
        return expr_alloc_comp(type, e->left.sym, sym);
    case E_LIST:
    case E_RANGE:
    case E_NONE:
        /* panic */;
    }
    return NULL;
}

tristate expr_calc_value(struct expr *e)
{
    tristate val1, val2;
    const char *str1, *str2;

    if (!e)
        return yes;

    switch (e->type) {
    case E_SYMBOL:
        sym_calc_value(e->left.sym);
        return e->left.sym->curr.tri;
    case E_AND:
        val1 = expr_calc_value(e->left.expr);
        val2 = expr_calc_value(e->right.expr);
        return EXPR_AND(val1, val2);
    case E_OR:
        val1 = expr_calc_value(e->left.expr);
        val2 = expr_calc_value(e->right.expr);
        return EXPR_OR(val1, val2);
    case E_NOT:
        val1 = expr_calc_value(e->left.expr);
        return EXPR_NOT(val1);
    case E_EQUAL:
        sym_calc_value(e->left.sym);
        sym_calc_value(e->right.sym);
        str1 = sym_get_string_value(e->left.sym);
        str2 = sym_get_string_value(e->right.sym);
        return !strcmp(str1, str2) ? yes : no;
    case E_UNEQUAL:
        sym_calc_value(e->left.sym);
        sym_calc_value(e->right.sym);
        str1 = sym_get_string_value(e->left.sym);
        str2 = sym_get_string_value(e->right.sym);
        return !strcmp(str1, str2) ? no : yes;
    default:
        printf("expr_calc_value: %d?\n", e->type);
        return no;
    }
}

static int expr_compare_type(enum expr_type t1, enum expr_type t2)
{
    if (t1 == t2)
        return 0;
    switch (t1) {
    case E_EQUAL:
    case E_UNEQUAL:
        if (t2 == E_NOT)
            return 1;
    case E_NOT:
        if (t2 == E_AND)
            return 1;
    case E_AND:
        if (t2 == E_OR)
            return 1;
    case E_OR:
        if (t2 == E_LIST)
            return 1;
    case E_LIST:
        if (t2 == 0)
            return 1;
    default:
        return -1;
    }
    printf("[%dgt%d?]", t1, t2);
    return 0;
}

static inline struct expr *
expr_get_leftmost_symbol(const struct expr *e)
{

    if (e == NULL)
        return NULL;

    while (e->type != E_SYMBOL)
        e = e->left.expr;

    return expr_copy(e);
}

/*
 * Given expression `e1' and `e2', returns the leaf of the longest
 * sub-expression of `e1' not containing 'e2.
 */
struct expr *expr_simplify_unmet_dep(struct expr *e1, struct expr *e2)
{
    struct expr *ret;

    switch (e1->type) {
    case E_OR:
        return expr_alloc_and(
            expr_simplify_unmet_dep(e1->left.expr, e2),
            expr_simplify_unmet_dep(e1->right.expr, e2));
    case E_AND: {
        struct expr *e;
        e = expr_alloc_and(expr_copy(e1), expr_copy(e2));
        e = expr_eliminate_dups(e);
        ret = (!expr_eq(e, e1)) ? e1 : NULL;
        expr_free(e);
        break;
        }
    default:
        ret = e1;
        break;
    }

    return expr_get_leftmost_symbol(ret);
}

void expr_print(struct expr *e, void (*fn)(void *, struct symbol *, const char *), void *data, int prevtoken)
{
    if (!e) {
        fn(data, NULL, "y");
        return;
    }

    if (expr_compare_type(prevtoken, e->type) > 0)
        fn(data, NULL, "(");
    switch (e->type) {
    case E_SYMBOL:
        if (e->left.sym->name)
            fn(data, e->left.sym, e->left.sym->name);
        else
            fn(data, NULL, "<choice>");
        break;
    case E_NOT:
        fn(data, NULL, "!");
        expr_print(e->left.expr, fn, data, E_NOT);
        break;
    case E_EQUAL:
        if (e->left.sym->name)
            fn(data, e->left.sym, e->left.sym->name);
        else
            fn(data, NULL, "<choice>");
        fn(data, NULL, "=");
        fn(data, e->right.sym, e->right.sym->name);
        break;
    case E_UNEQUAL:
        if (e->left.sym->name)
            fn(data, e->left.sym, e->left.sym->name);
        else
            fn(data, NULL, "<choice>");
        fn(data, NULL, "!=");
        fn(data, e->right.sym, e->right.sym->name);
        break;
    case E_OR:
        expr_print(e->left.expr, fn, data, E_OR);
        fn(data, NULL, " || ");
        expr_print(e->right.expr, fn, data, E_OR);
        break;
    case E_AND:
        expr_print(e->left.expr, fn, data, E_AND);
        fn(data, NULL, " && ");
        expr_print(e->right.expr, fn, data, E_AND);
        break;
    case E_LIST:
        fn(data, e->right.sym, e->right.sym->name);
        if (e->left.expr) {
            fn(data, NULL, " ^ ");
            expr_print(e->left.expr, fn, data, E_LIST);
        }
        break;
    case E_RANGE:
        fn(data, NULL, "[");
        fn(data, e->left.sym, e->left.sym->name);
        fn(data, NULL, " ");
        fn(data, e->right.sym, e->right.sym->name);
        fn(data, NULL, "]");
        break;
    default:
      {
        char buf[32];
        sprintf(buf, "<unknown type %d>", e->type);
        fn(data, NULL, buf);
        break;
      }
    }
    if (expr_compare_type(prevtoken, e->type) > 0)
        fn(data, NULL, ")");
}

static void expr_print_file_helper(void *data, struct symbol *sym, const char *str)
{
    xfwrite(str, strlen(str), 1, data);
}

void expr_fprint(struct expr *e, FILE *out)
{
    expr_print(e, expr_print_file_helper, out, E_NONE);
}

static void expr_print_gstr_helper(void *data, struct symbol *sym, const char *str)
{
    struct gstr *gs = (struct gstr*)data;
    const char *sym_str = NULL;

    if (sym)
        sym_str = sym_get_string_value(sym);

    if (gs->max_width) {
        unsigned extra_length = strlen(str);
        const char *last_cr = strrchr(gs->s, '\n');
        unsigned last_line_length;

        if (sym_str)
            extra_length += 4 + strlen(sym_str);

        if (!last_cr)
            last_cr = gs->s;

        last_line_length = strlen(gs->s) - (last_cr - gs->s);

        if ((last_line_length + extra_length) > gs->max_width)
            str_append(gs, "\\\n");
    }

    str_append(gs, str);
    if (sym && sym->type != S_UNKNOWN)
        str_printf(gs, " [=%s]", sym_str);
}

void expr_gstr_print(struct expr *e, struct gstr *gs)
{
    expr_print(e, expr_print_gstr_helper, gs, E_NONE);
}
